TI battery chips support cell phone fuel gauges

SAN DIEGO ( ChipWire) -- Texas Instruments Inc. will announce one of the first integrated "fuel-gauge" chips for cell phone batteries at the Power2000 battery conference this week.

Dallas-based TI said its new bq2019 will allow cellular handsets to accurately read the depletion curves of lithium-ion (Li-ion) and nickel-metal hydride (NiMH) batteries and report a battery's remaining charge as a percentage on an alphanumeric display.

Previous generations of so-called smart-battery ICs were geared toward portable computer batteries, and the small number of these ICs architected for cell phones enabled only a bar-length display. The more accurate fuel-gauging capability of the new IC will be particularly valuable in 3G phones, in which multimedia communication and Internet access are expected to be particularly taxing to a cell phone battery's life, said Dave Heacock, TI's business manager for battery-management products.

For years developers of smart-battery ICs have been in a "proselytization mode," Heacock said. Smart-battery ICs are effectively miniature data acquisition circuits that fit inside the shell of a laptop computer battery, and enable charge control and accurate fuel gauging of lithium-based batteries. TI acquired Benchmarq Microelectronics, a smart-battery IC pioneer, as part of its 1999 acquisition of Unitrode Corp. While the computer industry recognized that fuel gauging was an important feature, margin-stressed battery makers often passed on the feature in an effort to cut system costs.

But now some of the largest portable computer makers  Dell, Compaq and IBM  are providers of smart batteries, Heacock said. Smart-battery ICs are used in every Li-ion battery to minimize the dangers associated with overheating, Heacock said. NiMH batteries are also still widely used. Roughly 2.8 billion battery cells will be shipped each year that could benefit from the fuel gauging and charge control provided by smart-battery ICs, he said.

Three trends support the integration of smart batteries into cell phones, Heacock said. One is the integration of power switch functions on the same die with analog signal and digital control functions. The second trend is compressed packaging, wherein SOT packages dissipate more than an ampere of current. Bump chips and PowerPads  plastic SOT packages with metal bottoms  contribute to this trend.

The third item is the ability to integrate flash memory in a battery-management device. This enables a controller to remember a battery's precise charging and discharge pattern, and enables a calculated fuel gauge that matches the discharge curve of a battery.

The bq2019 Power Minder device integrates 96 bytes of flash, 32 of which serve as a shadow RAM for the controller. This allows the battery manager to save data about a system's power state, even as the battery itself runs down. The device itself consumes 80 microamps in an active state, and less than 1.5 microamps in sleep mode.

TI will also announce this week the bq2400X, a Li-ion charging controller. It includes a Schottky diode that provides reverse blocking for up to 1.2 A of charging current, and a power FET that serves as a series-pass element. The charge controller will support space-constrained systems with under 1,500 mA-hours of capacity, Heacock said.